The present invention relates to a knock control system for controlling ignition timing of an internal combustion engine in dependence upon occurrence of knock in the engine.
In the prior art, there is disclosed in Japanese Patent Laid-Open No. 46519/1984 or Japanese Patent Publication No. 42112/1988, for example, a system which is equipped with a microcomputer (as will be shortly referred to as "micom" for detecting the knocking accurately in addition to a microcomputer for controlling the same and which transmits the detected knock result from the knock detecting micom to the knock controlling micom.
In this prior art system, however, a knock sensor for detecting the knock to be encountered by an internal combustion engine is made separate from the knock detecting micom. As a result, the accurate knock detection may be impossible with the noise which may occur on the line connecting the knock sensor and the knock detecting micom. On the other hand, the knock detecting micom and the knock controlling micom are packaged in one engine control unit (as will be abbreviated into "ECU"), which may fail to have a sufficient space for packaging the micons.
In order to make the system entirely compact, on the other hand, it has been conceived to have the knock sensor packaged with a semiconductor circuit for detecting whether or not a knock is occurring (as is disclosed in Japanese Utility Model Registration Laid-Open No. 12831/1981, for example).
It is, therefore, conceivable to package the knock detecting micron integrally in the knock sensor.
In this system, however, the signal for transmitting the detected knock result from the knock detecting micom to the knock controlling micom is once outputted to the outside of the ECU so that the possibility of troubles will increase. In case the communicating signal lines are troubled, the knock controlling micom may decide that no knock has occurred, even if the knock detecting micom decides the occurrence of a knock.
The reason why this mistake happens will be described in the following. In case the detected knock result is expressed by the combination of the levels at ports Q.sub.2 and Q.sub.3 of the knock detecting sides of the communication signal lines between the knock detecting micom and the knock controlling micom, the result is enumerated in Table 1:
TABLE 1 ______________________________________ Detected Result No Low Medium High ______________________________________ Port Q.sub.2 0 1 0 1 Port Q.sub.3 0 0 1 1 ______________________________________
If either the ports Q.sub.2 or Q.sub.3 for outputting the detected knock result or the signal lines for the communication between the two micons are troubled to fix the ports Q.sub.2 and Q.sub.3 at 0, the knock controlling micom always decides that there is no knock. Then, there arises a problem that a retard control is not effected to damage the internal combustion engine even if a knock occurs.
In case, on the other hand, the knock sensor and the knock detecting micom are integrally packaged, the larger space for leading out the signal lines is required for the larger number of signal lines. Thus, there arises another problem that the space capacity is increased.